In order to answer to the needs of the French Navy, the thermal protective capacities of textile samples and protective garments are assessed under hot steam stress with a testing device developed in our institute. In a first series, textile samples are exposed to three conditions of hot steam jet (leading to three rates of heat flux: 4.31, 3.39, and 2.80 W/sq cm) and to a hot saturated environment (80 deg C and 100% of relative humidity leading to a heat flux of 0.70 W/sq cm). In a second series, protective garments are tested in a hot saturated environment (80 deg C and 100% of relative humidity) on a thermal manikin. With the same thickness or inferior one, the textile samples and garments impermeable to water vapour are more efficient to limit the heat transfer due to hot steam stress exposure than the permeable ones. Moreover, thicker is the sample or the garment, higher is the thermal protection it gives. But, there is a maximal thickness over which the gain of protection is not enough sufficient to justify the increase of thickness. The diffusion of the water vapour through the textile samples and its absorption bring additional heat and decrease the protective capacities of the textile fabrics. This mechanism observed with the permeable samples at the beginning of the exposure to hot steam jets and should be take into account to evaluate the samples or the garments to avoid skin burn. This mechanism is also observed with one impermeable sample after a time delay of exposure (depending on the steam conditions and the textile) probably due to a denaturation of the impermeability of the sample. In conclusion, the best protection against hot water steam stress should be given by a thick, multi-layered and impermeable to water vapour garment with a wide cut to limit the contact with the skin.